Causes of Solid-Appearing Lumps & Bumps on the Skin in Cats
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Causes of Solid-Appearing Lumps and Bumps on the Skin in Cats Causes of Solid-Appearing Lumps and Bumps on the Skin in Cats

Cats can develop small bumps (papules) or larger lumps (nodules) on their skin. The term 'tumor' means an abnormal growth or swelling, and is often used to designate cancer. Often the word 'lump' also brings the word 'cancer' to mind. There are, however, many other causes of lumps and bumps. The following table includes most of the conditions which result in solid lumps and bumps. The list is rather extensive, so you can understand why a quick diagnosis may be difficult to make and various diagnostic tests, such as biopsies, may need to be performed. The most common causes of solid lumps and bumps are color-coded gray in the table (some may be more common in certain geographical areas).

Condition Description Symptoms Diagnosis Treatment
Abscesses Accumulation of pus; may or may not be caused by an infection; in cats, often due to bite wounds These may appear as firm, fluid-filled nodules of varying shapes and sizes, with a small crusty area at puncture site; if due to infection, cat may have fever, loss of appetite, depression; may open and drain History, physical exam, needle aspirate Surgically open, drain and flush; if infected, administer appropriate antibiotics

Allergic and irritant contact dermatitis

An allergic reaction following exposure to antibiotics applied to the skin; metals such as nickel; materials such as rubber, wool, and plastic; and chemicals such as dyes and carpet deodorizers; or inflammation caused by irritating substances such as poison ivy. Generally requires multiple exposures.

Red skin and small bumps or blisters on the areas of skin that are sparsely haired and directly exposed to the offending substance, itching; hair loss in chronic conditions

Patch test, exclusion trials

Restrict exposure to the allergen or contact irritant in the cat's environment; steroids, antihistamines

Apocrine sweat gland cyst Rare in cats Single, round, smooth nodules with no hair; may appear bluish; usually filled with a watery liquid; most common on head, neck, and limbs Physical exam; biopsy Surgical removal is optional
Basal cell tumors Most common skin tumor in cats; benign tumors which may become cancerous, slow-growing tumors which rarely metastasize Single, sometimes fluid-filled nodules which may ulcerate; usually on the head, neck, and chest; may be hyperpigmented Biopsy Surgical removal (if benign, surgical removal is optional)
Bee, wasp, hornet stings Skin reactions can vary dramatically in severity Immediately after the bite, see swelling, redness, pain, possibly itching; subsequently may develop extensive ulcers with draining; may develop hives or anaphylaxis History, physical exam Antihistamines, steroids; wet dressings if ulcerated; protect the area from self-inflicted trauma
Benign tumors See specific type, e.g., Fibromas, Lipomas, Basal cell tumors      

Chiggers (harvest mites)

Seasonal disease caused by larvae of the chigger

Itching, bumps usually on feet, abdomen, folds at base of ears

Visualization of mite larvae or microscopic examination of skin scraping


Coccidioidomycosis Caused by the fungus Coccidioides immitis found in the soil in the Southwestern U.S. Draining nodules, fever, weight loss; unlike dogs, no respiratory signs Microscopic examination of drainage; blood test Ketoconazole, itraconazole
Cryptococcosis Fungal infection often transmitted through bird droppings; more common in cats with suppressed immune systems Nodules often over the nose which may ulcerate; many other signs depending on what other body systems are infected Microscopic exam of discharge, blood tests, culture, biopsy; look for underlying cause of immunosuppression Itraconazole
Cutaneous horn Benign growths of hard tissue which look like small horns; cause unknown, though may be associated with some underlying disease such as cancers, follicular cysts, or FeLV   to 2 inch hard horn-like growths; may be single or multiple; in cats may occur on foot pads Clinical appearance; look for underlying cause Surgical removal
Cuterebra Caused by the 1-1  inch larva of the Cuterebra fly; usually seen in late summer Nodule forms around the larva; usually found on the head and neck; nodule has a small opening through which the larva breathes and will eventually escape Clinical signs; opening the nodule and finding the larva Surgically open the nodule and remove the larva; do NOT squeeze the nodule or break up the larva or a severe allergic reaction may occur
Drug or injection reaction Rare skin reaction to a drug which is inhaled, given orally or applied topically; more common with penicillins, sulfonamides, and cephalosporins; usually occurs within 2 weeks of giving the drug Can vary widely and may include itching, hair loss, redness, swelling, papules, crusts, ulcers, and draining wounds History of being treated with a drug, symptoms, biopsy Discontinue offending drug; treat symptomatically
Epitheliotropic lymphoma (mycosis fungoides) Rare cancer of T lymphocytes seen in older cats; may be associated with FeLV Redness, itching, scales, ulcerated nodules Needle or other biopsy Poor response to treatments which include chemotherapy, surgical removal, retinoids, fatty acids
Feline acne Skin condition of unknown cause which may occur as single episode or continue as chronic condition; most commonly seen on the chin; can develop into a more serious, deep infection if not treated Comedones (black heads) on lips and chin, later developing pustules and small nodules; may itch - especially in chronic cases; chin may become swollen; can become secondarily infected Physical exam; tests to rule out underlying causes or diseases with similar symptoms; skin biopsy Mild: antiseborrheic shampoos, antibacterial creams, topical Vitamin A; Severe: antibiotics, fatty acids, retinoids (use with caution, can be irritating)
Feline leprosy Caused by the bacteria 'Mycobacterium'; usually seen in young cats Single or multiple nodules which may drain; usually on head or neck; nonpainful; cat does not show other signs of disease Biopsy, culture Surgical removal, anti-mycobacterial drugs such as rifampin or clofazimine
Feline pox Viral disease; outdoor cats more commonly affected; presumably transmitted by bite wounds Nodule at the site of a previous bite wound; progresses to multiple nodules which may ulcerate and have crusts; may itch History, physical exam; biopsy; specialized testing to identify the virus Lesions usually resolve in 3-4 weeks; antibiotics for any secondary infection; antihistamines for itching; no steroids; in some cats, lesions progress and do not respond to treatment
Fibroma Uncommon benign tumor Single nodule with a pedicle, usually on legs, groin, or sides Biopsy Surgical removal is optional
Fibrosarcoma Rapidly growing, invasive tumor; may occur at the site of a vaccination or injection, especially in cats; may be induced by a form of FeLV Irregular-shaped, firm nodule; may ulcerate Biopsy Surgical removal, however, since tumor is invasive need to remove large area around tumor, sometimes including large masses of muscle and bone; if tumor is on a leg, amputation of the leg is commonly recommended; surgery may be combined with chemotherapy and radiation
Follicular cyst Most common cyst; may be called 'sebaceous cysts' by some veterinarians Single, round nodules on or underneath the skin; may appear bluish; may contain a thick yellowish to gray material; usually found on the head, neck, and trunk Biopsy Surgical removal optional; do NOT squeeze these cysts since a severe skin reaction will occur
Granulomas May be due to infections; the body's reaction to foreign material such as plant material (e.g., foxtail) and suture material; other constant irritation; or unknown causes Solid, firm nodules of varying sizes; those due to foreign bodies often have draining tracts; may develop hair loss, ulcers, and secondary infections History, clinical signs, biopsy, surgical exploratory Surgical removal of the foreign body (in the case of plant material, tracts may be extensive and require major surgery); antibiotics if infected; treat any other underlying cause
Hemangiosarcoma Malignant, invasive tumor more common on sun-damaged skin Blue to reddish black nodule; usually on ears, head, legs, groin, and axillae; often ulcerate Biopsy Surgical removal; need to remove large area around the tumor; if tumor is on a leg, amputation of the leg is commonly recommended
Hematoma Localized collection of blood that has leaked out of blood vessels, e.g., bruise These may appear as firm, fluid-filled nodules of varying shapes and sizes Needle aspirate Depending on location and size may resolve on their own, or need drainage
Histoplasmosis Fungal infection which can rarely cause skin lesions Ulcerated and draining nodules; most commonly see respiratory and gastrointestinal symptoms Needle aspirate or biopsy Ketoconazole, itraconazole


Infection with the larvae (immature forms) of hookworms

Red bumps, usually on feet, rough foot pads, abnormal nail growth, itching

Physical exam, history of poor sanitation

Treat for intestinal infection; move cat to different environment

Lichenoid dermatosis Often a response to other underlying disease such as fleas or bacterial infections Small, flat nodules with thick surfaces Biopsy, look for underlying disease Treat underlying cause; this reaction usually resolves on its own
Lipoma Uncommon benign fatty tumor Usually single, soft, domed nodule; can become very large Fine needle biopsy Surgical removal if large or interferes with movement


Type of cancer; may occur in other organs without skin involvement

Nodules with ulcers; redness


Surgery, chemotherapy, radiation; lymphoma of the skin does not usually respond to treatment as well as other lymphomas

Mammary cancer Most common in unspayed females; in cats, 85% are malignant Single or multiple nodules under the skin, of varying sizes, often irregular in shape; may ulcerate and drain Biopsy Surgical removal
Mast cell tumor Common cancer which is graded from 1-4: Grade 1 is one slow-growing tumor, and Grade 4 is rapidly growing malignant tumors with metastasis; in cats, most are Grade 1 Tumors may be of various sizes, appearances, and numbers Biopsy to grade the tumors which determines treatment and prognosis Depends upon grade; surgical removal, taking large area around tumor; chemotherapy; prednisone; radiation
Melanoma Malignant tumor; uncommon in cats Usually single, dark-colored nodule which often ulcerates Biopsy Surgical removal, taking large area around tumor
Miliary dermatitis in cats Part of the common eosinophilic allergic syndrome in cats which includes eosinophilic granulomas, eosinophilic plaques, and rodent ulcers; may also be associated with infections, autoimmune diseases, hormonal disorders, and nutritional deficiencies Multiple, small, crusty bumps, usually over hips, neck, and back of thighs; moderate to severe itching Microscopic examination of swab from lesion, biopsy, CBC (find increased eosinophils); look for underlying cause, e.g., parasites, food allergy, atopy Treat underlying cause if found; corticosteroids; fatty acid supplements
Mosquito bite hypersensitivity Severe allergic reaction to mosquito bites; lesions most common on nose and ear tips - also footpads, lips, and chin Acute lesions are red, raised, and oozing; with time develop hair loss, scales, nodules, and pigment changes; some cats develop fever and swollen lymph nodes History of exposure to mosquitoes; lesions resolve when cat is hospitalized or otherwise restricted from exposure to mosquitoes Restrict exposure to mosquitoes, insect repellents, prednisone
Nevi Usually benign lesions; some types may indicate the presence of an underlying disease Well-delineated, firm nodules, often multiple and on the head and neck Biopsy Surgical removal, although recurrence is common; depending upon the type, look for underlying disease
Nocardia Bacterial infection usually acquired from a puncture wound Usually see respiratory signs; skin lesions include draining nodules Bacterial culture, microscopic examination of drainage Poor prognosis; antibiotics
Panniculitis May be caused by trauma, foreign bodies, infections, autoimmune diseases, or unknown causes Deep-seated nodules, often ulcerated and draining; usually on the body vs. the head or limbs; may see loss of appetite, depression Microscopic exam of drainage; biopsy; tests to rule out other causes Surgical removal; if multiple lesions, prednisone and Vitamin E; may need long-term treatment
Phaeohyphomycosis Caused by wound contamination with a fungus A single nodule on the legs or multiple ulcerated and draining nodules over the body Microscopic examination of drainage, culture, biopsy Surgical removal though often recur; possible antifungal medications
Pyoderma-deep Bacterial infections of skin and underlying tissue often secondary to another skin disease such as self-inflicted trauma, wounds, acral lick granulomas, allergies, seborrhea Ulcerated pustules or nodules, draining tracts, crusts, thickened skin Skin scrapings, biopsy, culture Clip and cleanse area; antibiotics, prevent self-trauma (licking, scratching), NO steroids
Pythiosis Caused by an aquatic mold Ulcerated draining nodules on the legs, head, and base of tail which may itch; often see other signs of illness due to infection of the gastrointestinal tract Microscopic examination of drainage; biopsy Often fatal; surgical removal
Sebaceous gland cyst Extremely rare Firm nodules, usually less than   inch in diameter Biopsy Surgical removal
Sebaceous gland tumor Rare in cats; rarely spreads or recurs; several types Nodules which may ulcerate; usually on the head and legs Biopsy Surgical removal if invasive; if a benign lesion, removal is optional
Skin cancer See specific type, e.g., Fibrosarcoma, Melanoma, Squamous cell carcinoma, Mast cell tumor, Lymphoma      
Spider bites/eosinophilic folliculitis Bites from some spiders and caterpillars contain strong toxins; usually appear on the nose of dogs and paws of cats Immediately after the bite, swelling, redness, pain; subsequently may develop extensive ulcers with draining History, biopsy Corticosteroids, wet dressings, protect the area from self-inflicted trauma; may develop permanent loss of hair and scarring
Sporotrichosis Caused by the fungus Sporothrix schenckii which generally enters through a puncture wound Raised nodules with multiple draining tracts; cats may develop fever, depression, and loss of appetite Microscopic exam of drainage; culture; fluorescent antibody test Potassium iodide, ketoconazole, itraconazole
Squamous cell carcinoma Common malignant tumor; may occur more commonly in sun-damaged or chronically irritated skin Two forms: cauliflower-like lesions, often ulcerated more common on ears; crusted ulcers on head or feet (around claws) Biopsy Surgical removal, radiation, hyperthermia
Tick bites Ticks cause a local inflammation in the skin, even when the entire tick is removed Nodule and redness at site of the bite; may itch and develop crusts; may last several months History Remove the tick; use a tick preventive; allow nodule to resolve on its own
Urticaria (hives) Reaction, often allergic, to insect bite, drug, vaccine, sunlight, etc. Multiple swellings, with hair standing up over swellings; may itch History, physical exam Often resolves on its own; in the case of allergic reactions, antihistamines, epinephrine, or corticosteroids depending upon severity
Xanthoma Result of abnormality in lipid metabolism; can be a result of diabetes mellitus or due to hereditary affecting lipid metabolism (hyperlipidaemia) White or yellow nodules, usually on head, extremities, and bony prominences; often painful and itchy Physical exam and history; biopsy; Treat underlying disease; change diet; lesions often recur if surgically removed
Zygomycosis Uncommon fungal disease Draining nodules; may also see pneumonia, vomiting, or jaundice depending upon the body organs involved Microscopic examination of the drainage; biopsy Often fatal; surgical removal of nodules followed by amphotericin B, benzimidazoles, or potassium iodide


Birchard, SJ; Sherding, RG (eds.) Saunders Manual of Small Animal Practice. W.B. Saunders Co. Philadelphia, PA; 1994.

Greene, CE (ed.) Infectious Diseases of the Dog and Cat. W.B. Saunders Co. Philadelphia, PA; 1998.

Griffin, C; Kwochka, K; Macdonald, J. Current Veterinary Dermatology. Mosby Publications. Linn, MO; 1993.

McKeever, PJ; Harvey, RG. Skin Diseases of the Dog and Cat. Iowa State University Press. Ames, Iowa; 1998.

Paterson, S. Skin Diseases of the Cat. Blackwell Science Ltd. London, England; 2000.

Paterson, S. Skin Diseases of the Dog. Blackwell Science Ltd. London, England; 1998.

Scott, D; Miller, W; Griffin, C. Muller and Kirk's Small Animal Dermatology. W.B. Saunders Co. Philadelphia, PA; 1995.

References and Further Reading

Birchard, SJ; Sherding, RG (eds.) Saunders Manual of Small Animal Practice. W.B. Saunders Co. Philadelphia, PA; 1994.

Greene, CE (ed.) Infectious Diseases of the Dog and Cat. W.B. Saunders Co. Philadelphia, PA; 1998.

Griffin, C; Kwochka, K; Macdonald, J. Current Veterinary Dermatology. Mosby Publications. Linn, MO; 1993.

McKeever, PJ; Harvey, RG. Skin Diseases of the Dog and Cat. Iowa State University Press. Ames, Iowa; 1998.

Paterson, S. Skin Diseases of the Cat. Blackwell Science Ltd. London, England; 2000.

Paterson, S. Skin Diseases of the Dog. Blackwell Science Ltd. London, England; 1998.

Scott, D; Miller, W; Griffin, C. Muller and Kirk's Small Animal Dermatology. W.B. Saunders Co. Philadelphia, PA; 1995.

   Click here for the web viewable version of this article.

Click here to email this article to a friend.

Copyright © 1997-2017, Foster & Smith, Inc. All Rights Reserved.
Reprinted from